1. Field of the Invention
The present invention relates to beam guidance systems for projectiles and the like, and, more particularly, to a beam modulating device for coding the projected beam with information enabling a receiver in the projectile to determine what the position of the projectile is in the beam cross section.
2. Description of the Prior Art
In this type of system, a spatially coded beam of electromagnetic energy, such as a laser, is received and read by a rearward facing receiver in a projectile during its flight to the target. Basically, the beam is pointed at the target from a projectile launching position, and a projectile flight control system uses the detected beam information to direct the projectile along the centerline of the beam. The launching site may be on an aircraft, on land or on sea, for example. Some systems, such as the present one, provide the projectile position information in the form of two directional signals--namely, an elevation signal and an azimuth signal.
Several such guidance schemes have been proposed and tested using a rotating disc in the path of the beam, the disc containing a particular pattern of light-passing and light-blocking portions which, together with stored or received reference information, will enable the receiver to tell at which fraction of the horizontal field or vertical field it may be located at that instant. Generally two such beams or discs are required, one for each flight control axis of the projectile.
The usual known systems are not adapted to the simultaneous control of multiple missiles against multiple targets. Further, many present systems are seriously affected by environmental light conditions including smoke, dust, or turbulence, in the intervening atmosphere. Others use impractical or complex modulation and/or decoding schemes.
U.S. Pat. No. 4,014,482 to Esker et al discloses a laser beam rider missile director using a rotating light chopper or reticle with opaque and transparent bar portions for coding the beam. The reticle has a center which is rotated around the center of the transmitted beam. The beam is pulsed at two different rates and coordinated with the reticle position to provide the missile receiver with magnitude and phase components to use in determining the missile position with respect to the beam centerline.
U.S. Pat. No. 2,942,118 to Gedance discloses a tracking system similar in general concept to the Esker et al system, that is, a patterned reticle wheel has an axis which is displaced from and rotates around the optical axis or centerline of the radiant energy beam.
U.S. Pat. No. 3,513,315 to Sundstrom et al uses a reticle pattern which nutates a beam of light about the line of sight without rotating about its own axis.
U.S. Pat. No. 4,178,505 to Skagerlund discloses a tracking device with a rotating mask having a modified radial type of light-forming pattern, used to measure target position in polar coordinates.
U.S. Pat. No. 3,950,099 to Malueg discloses a two-axis "motion detector" having a single rotating disc with two patterns thereon, for modulating a beam at two different frequencies.
U.S. Pat. No. 3,957,377 to Hutchinson discloses a position sensing arrangement of two beam signal patterns in a disc, utilizing a varying cross-section area of the beam.
U.S. Pat. No. 4,186,899 to Stewart discloses an oscillating mirror and chopper arrangement for projecting two rectangular beams in respective horizontal and vertical scanning directions.
While it is possible that more pertinent prior art exists, Applicant's search is believed to have been conducted with a conscientious effort to locate and evaluate the most relevant art available at the time, but this statement is not be be construed as a representation that no more pertinent art exists.